We modeled the radiative forcing (RF) of sulfate aerosols and water vapor (WV) clouds generated by the explosive eruption of the Hunga volcano on January 15, 2022, using the WRF-Chem meteorology–chemistry model. We injected 150 Mt of WV and 0.45 Mt of SO2 at a height of 35 km. The resulting volcanic WV layer was cooled through thermal radiation and descended to 27 km in two weeks. The WV mixing ratio within the plume exceeded 30 ppmV after the eruption, gradually reducing after that. Within three weeks, SO2 had been converted to SO4 with a 1.0 µm global stratospheric aerosol optical depth (SAOD) of 0.0025. To fit the observed SAOD, the SO2 mass should be scaled to 0.73–1.46 Mt. The six-month-average global mean net instantaneous RF (IRF) of volcanic sulfate aerosols (SAs) at the top of the atmosphere (TOA) reaches −0.381 W/m2 for 1.46-Mt SO2 emission. The negative WV net IRF at TOA is at least one order of magnitude smaller than that from SAs. The WV IRF at the bottom of the atmosphere is negligibly small and cannot cause discernable long-term effects on climate. Broadband WV calculations overestimate IRF by 30% relative to line-by-line calculations. Cooling in the lower stratosphere within the WV plume exceeds −1 K, and the WV adjusted (to stratospheric temperature) RF (ARF) is positive at TOA and the tropopause but overwhelmed by negative SA forcing. The patchy tropospheric temperature response does not show systematic changes.